require_relative "column_method_definer"
require_relative "scope_method_definer"
require_relative "top_of_list_method_definer"
require_relative "add_new_at_method_definer"
require_relative "aux_method_definer"
require_relative "callback_definer"

module ActiveRecord
  module Acts #:nodoc:
    module List #:nodoc:
      def self.included(base)
        base.extend(ClassMethods)
      end

      # This +acts_as+ extension provides the capabilities for sorting and reordering a number of objects in a list.
      # The class that has this specified needs to have a +position+ column defined as an integer on
      # the mapped database table.
      #
      # Todo list example:
      #
      #   class TodoList < ActiveRecord::Base
      #     has_many :todo_items, order: "position"
      #   end
      #
      #   class TodoItem < ActiveRecord::Base
      #     belongs_to :todo_list
      #     acts_as_list scope: :todo_list
      #   end
      #
      #   todo_list.first.move_to_bottom
      #   todo_list.last.move_higher
      module ClassMethods

        # Configuration options are:
        #
        # * +column+ - specifies the column name to use for keeping the position integer (default: +position+)
        # * +scope+ - restricts what is to be considered a list. Given a symbol, it'll attach <tt>_id</tt>
        #   (if it hasn't already been added) and use that as the foreign key restriction. It's also possible
        #   to give it an entire string that is interpolated if you need a tighter scope than just a foreign key.
        #   Example: <tt>acts_as_list scope: 'todo_list_id = #{todo_list_id} AND completed = 0'</tt>
        # * +top_of_list+ - defines the integer used for the top of the list. Defaults to 1. Use 0 to make the collection
        #   act more like an array in its indexing.
        # * +add_new_at+ - specifies whether objects get added to the :top or :bottom of the list. (default: +bottom+)
        #                   `nil` will result in new items not being added to the list on create.
        def acts_as_list(options = {})
          configuration = { column: "position", scope: "1 = 1", top_of_list: 1, add_new_at: :bottom}
          configuration.update(options) if options.is_a?(Hash)

          caller_class = self

          ColumnMethodDefiner.call(caller_class, configuration[:column])
          ScopeMethodDefiner.call(caller_class, configuration[:scope])
          TopOfListMethodDefiner.call(caller_class, configuration[:top_of_list])
          AddNewAtMethodDefiner.call(caller_class, configuration[:add_new_at])

          AuxMethodDefiner.call(caller_class)
          CallbackDefiner.call(caller_class, configuration[:add_new_at])

          include ::ActiveRecord::Acts::List::InstanceMethods
        end
      end

      # All the methods available to a record that has had <tt>acts_as_list</tt> specified. Each method works
      # by assuming the object to be the item in the list, so <tt>chapter.move_lower</tt> would move that chapter
      # lower in the list of all chapters. Likewise, <tt>chapter.first?</tt> would return +true+ if that chapter is
      # the first in the list of all chapters.
      module InstanceMethods
        # Insert the item at the given position (defaults to the top position of 1).
        def insert_at(position = acts_as_list_top)
          insert_at_position(position)
        end

        # Swap positions with the next lower item, if one exists.
        def move_lower
          return unless lower_item

          acts_as_list_class.transaction do
            if lower_item.send(position_column) != self.send(position_column)
              swap_positions(lower_item, self)
            else
              lower_item.decrement_position
              increment_position
            end
          end
        end

        # Swap positions with the next higher item, if one exists.
        def move_higher
          return unless higher_item

          acts_as_list_class.transaction do
            if higher_item.send(position_column) != self.send(position_column)
              swap_positions(higher_item, self)
            else
              higher_item.increment_position
              decrement_position
            end
          end
        end

        # Move to the bottom of the list. If the item is already in the list, the items below it have their
        # position adjusted accordingly.
        def move_to_bottom
          return unless in_list?
          acts_as_list_class.transaction do
            decrement_positions_on_lower_items
            assume_bottom_position
          end
        end

        # Move to the top of the list. If the item is already in the list, the items above it have their
        # position adjusted accordingly.
        def move_to_top
          return unless in_list?
          acts_as_list_class.transaction do
            increment_positions_on_higher_items
            assume_top_position
          end
        end

        # Removes the item from the list.
        def remove_from_list
          if in_list?
            decrement_positions_on_lower_items
            set_list_position(nil)
          end
        end

        # Move the item within scope. If a position within the new scope isn't supplied, the item will
        # be appended to the end of the list.
        def move_within_scope(scope_id)
          send("#{scope_name}=", scope_id)
          save!
        end

        # Increase the position of this item without adjusting the rest of the list.
        def increment_position
          return unless in_list?
          set_list_position(self.send(position_column).to_i + 1)
        end

        # Decrease the position of this item without adjusting the rest of the list.
        def decrement_position
          return unless in_list?
          set_list_position(self.send(position_column).to_i - 1)
        end

        def first?
          return false unless in_list?
          !higher_item
        end

        def last?
          return false unless in_list?
          !lower_item
        end

        # Return the next higher item in the list.
        def higher_item
          return nil unless in_list?
          higher_items(1).first
        end

        # Return the next n higher items in the list
        # selects all higher items by default
        def higher_items(limit=nil)
          limit ||= acts_as_list_list.count
          position_value = send(position_column)
          acts_as_list_list.
            where("#{quoted_position_column_with_table_name} <= ?", position_value).
            where("#{quoted_table_name}.#{self.class.primary_key} != ?", self.send(self.class.primary_key)).
            order("#{quoted_position_column_with_table_name} DESC").
            limit(limit)
        end

        # Return the next lower item in the list.
        def lower_item
          return nil unless in_list?
          lower_items(1).first
        end

        # Return the next n lower items in the list
        # selects all lower items by default
        def lower_items(limit=nil)
          limit ||= acts_as_list_list.count
          position_value = send(position_column)
          acts_as_list_list.
            where("#{quoted_position_column_with_table_name} >= ?", position_value).
            where("#{quoted_table_name}.#{self.class.primary_key} != ?", self.send(self.class.primary_key)).
            order("#{quoted_position_column_with_table_name} ASC").
            limit(limit)
        end

        # Test if this record is in a list
        def in_list?
          !not_in_list?
        end

        def not_in_list?
          send(position_column).nil?
        end

        def default_position
          acts_as_list_class.columns_hash[position_column.to_s].default
        end

        def default_position?
          default_position && default_position.to_i == send(position_column)
        end

        # Sets the new position and saves it
        def set_list_position(new_position)
          write_attribute position_column, new_position
          save(validate: false)
        end

        private

          def swap_positions(item1, item2)
            item1.set_list_position(item2.send(position_column))
            item2.set_list_position(item1.send("#{position_column}_was"))
          end

          def acts_as_list_list
            acts_as_list_class.unscoped do
              acts_as_list_class.where(scope_condition)
            end
          end

          # Poorly named methods. They will insert the item at the desired position if the position
          # has been set manually using position=, not necessarily the top or bottom of the list:

          def add_to_list_top
            if not_in_list? || internal_scope_changed? && !position_changed || default_position?
              increment_positions_on_all_items
              self[position_column] = acts_as_list_top
            else
              increment_positions_on_lower_items(self[position_column], id)
            end

            # Make sure we know that we've processed this scope change already
            @scope_changed = false

            # Don't halt the callback chain
            true
          end

          def add_to_list_bottom
            if not_in_list? || internal_scope_changed? && !position_changed || default_position?
              self[position_column] = bottom_position_in_list.to_i + 1
            else
              increment_positions_on_lower_items(self[position_column], id)
            end

            # Make sure we know that we've processed this scope change already
            @scope_changed = false

            # Don't halt the callback chain
            true
          end

          # Overwrite this method to define the scope of the list changes
          def scope_condition() {} end

          # Returns the bottom position number in the list.
          #   bottom_position_in_list    # => 2
          def bottom_position_in_list(except = nil)
            item = bottom_item(except)
            item ? item.send(position_column) : acts_as_list_top - 1
          end

          # Returns the bottom item
          def bottom_item(except = nil)
            conditions = except ? "#{quoted_table_name}.#{self.class.primary_key} != #{self.class.connection.quote(except.id)}" : {}
            acts_as_list_list.in_list.where(
              conditions
            ).order(
              "#{quoted_position_column_with_table_name} DESC"
            ).first
          end

          # Forces item to assume the bottom position in the list.
          def assume_bottom_position
            set_list_position(bottom_position_in_list(self).to_i + 1)
          end

          # Forces item to assume the top position in the list.
          def assume_top_position
            set_list_position(acts_as_list_top)
          end

          # This has the effect of moving all the higher items up one.
          def decrement_positions_on_higher_items(position)
            acts_as_list_list.where("#{quoted_position_column_with_table_name} <= ?", position).decrement_all
          end

          # This has the effect of moving all the lower items up one.
          def decrement_positions_on_lower_items(position=nil)
            return unless in_list?
            position ||= send(position_column).to_i
            acts_as_list_list.where("#{quoted_position_column_with_table_name} > ?", position).decrement_all
          end

          # This has the effect of moving all the higher items down one.
          def increment_positions_on_higher_items
            return unless in_list?
            acts_as_list_list.where("#{quoted_position_column_with_table_name} < #{send(position_column).to_i}").increment_all
          end

          # This has the effect of moving all the lower items down one.
          def increment_positions_on_lower_items(position, avoid_id = nil)
            avoid_id_condition = avoid_id ? " AND #{quoted_table_name}.#{self.class.primary_key} != #{self.class.connection.quote(avoid_id)}" : ''

            acts_as_list_list.where("#{quoted_position_column_with_table_name} >= #{position}#{avoid_id_condition}").increment_all
          end

          # Increments position (<tt>position_column</tt>) of all items in the list.
          def increment_positions_on_all_items
            acts_as_list_list.increment_all
          end

          # Reorders intermediate items to support moving an item from old_position to new_position.
          def shuffle_positions_on_intermediate_items(old_position, new_position, avoid_id = nil)
            return if old_position == new_position
            avoid_id_condition = avoid_id ? " AND #{quoted_table_name}.#{self.class.primary_key} != #{self.class.connection.quote(avoid_id)}" : ''

            if old_position < new_position
              # Decrement position of intermediate items
              #
              # e.g., if moving an item from 2 to 5,
              # move [3, 4, 5] to [2, 3, 4]
              acts_as_list_list.where(
                "#{quoted_position_column_with_table_name} > ?", old_position
              ).where(
                "#{quoted_position_column_with_table_name} <= #{new_position}#{avoid_id_condition}"
              ).decrement_all
            else
              # Increment position of intermediate items
              #
              # e.g., if moving an item from 5 to 2,
              # move [2, 3, 4] to [3, 4, 5]
              acts_as_list_list.where(
                "#{quoted_position_column_with_table_name} >= ?", new_position
              ).where(
                "#{quoted_position_column_with_table_name} < #{old_position}#{avoid_id_condition}"
              ).increment_all
            end
          end

          def insert_at_position(position)
            return set_list_position(position) if new_record?
            with_lock do
              if in_list?
                old_position = send(position_column).to_i
                return if position == old_position
                shuffle_positions_on_intermediate_items(old_position, position)
              else
                increment_positions_on_lower_items(position)
              end
              set_list_position(position)
            end
          end

          # used by insert_at_position instead of remove_from_list, as postgresql raises error if position_column has non-null constraint
          def store_at_0
            if in_list?
              old_position = send(position_column).to_i
              set_list_position(0)
              decrement_positions_on_lower_items(old_position)
            end
          end

          def update_positions
            old_position = send("#{position_column}_was") || bottom_position_in_list + 1
            new_position = send(position_column).to_i

            return unless acts_as_list_list.where(
              "#{quoted_position_column_with_table_name} = #{new_position}"
            ).count > 1
            shuffle_positions_on_intermediate_items old_position, new_position, id
          end

          def internal_scope_changed?
            return @scope_changed if defined?(@scope_changed)

            @scope_changed = scope_changed?
          end

          def clear_scope_changed
            remove_instance_variable(:@scope_changed) if defined?(@scope_changed)
          end

          def check_scope
            if internal_scope_changed?
              cached_changes = changes

              cached_changes.each { |attribute, values| self[attribute] = values[0] }
              send('decrement_positions_on_lower_items') if lower_item
              cached_changes.each { |attribute, values| self[attribute] = values[1] }

              send("add_to_list_#{add_new_at}") if add_new_at.present?
            end
          end

          # This check is skipped if the position is currently the default position from the table
          # as modifying the default position on creation is handled elsewhere
          def check_top_position
            if send(position_column) && !default_position? && send(position_column) < acts_as_list_top
              self[position_column] = acts_as_list_top
            end
          end

          # When using raw column name it must be quoted otherwise it can raise syntax errors with SQL keywords (e.g. order)
          def quoted_position_column
            @_quoted_position_column ||= self.class.connection.quote_column_name(position_column)
          end

          # Used in order clauses
          def quoted_table_name
            @_quoted_table_name ||= acts_as_list_class.quoted_table_name
          end

          def quoted_position_column_with_table_name
            @_quoted_position_column_with_table_name ||= "#{quoted_table_name}.#{quoted_position_column}"
          end
      end
    end
  end
end